Correction: In last month’s newsletter (August 2007), the Outbreak Spotlight article stated that norovirus “Illness is typically self-limiting and is treatable with antibiotics.” The sentence should have read “Illness is typically self-limiting and is NOT treatable with antibiotics.”

Sandra Gorsuch, MSField Epidemiologist District 5

Background

On December 18, 2006, a representative of the Shelby County Health Department (SCHD) notified the Indiana State Department of Health (ISDH) that at least 19 of 56 (33%) residents at Ashford Place, a local long-term care facility, were experiencing symptoms of gastroenteritis, including nausea, vomiting, diarrhea, and fever.

Epidemiologic Investigation

The ISDH and the SCHD initiated a collaborative investigation to determine the cause of the outbreak and implement control measures to prevent further transmission of the illness. The investigation revealed that 26 residents (46%) were experiencing nausea, vomiting, or diarrhea, and some had low-grade fever. Two of the symptomatic residents were hospitalized. Four residents submitted stool specimens to the ISDH Laboratories for analysis (see Laboratory Results). Generally, illness self-resolved within 48 hours. None of the facility medical or dietary staff were ill. The pattern of illness onset dates, as well as the fact that no staff members were ill, indicated that the outbreak was most likely person to person rather than foodborne or related to another point source.

Environmental Assessment

Given no facility inspection was conducted the apparent person-to-person transmission route of the outbreak, the ISDH and the SCHD recommended disinfecting facility environmental surfaces with a 1:10 chlorine bleach to water solution, isolating ill residents, discontinuing the use of hand gels, thoroughly washing hands with warm water and soap for at least 20 seconds between residents, and changing gloves between residents when performing medical procedures. Facility staff initiated use of surgical masks while caring for residents and restricted visitation. After implementation of these control measures, only nine ill residents were reported as of December 19, 2006.

Conclusions

The investigation confirmed that an outbreak of viral gastroenteritis occurred at Ashford Place beginning December 17, 2006. The causative agent of this outbreak was Norovirus. The sudden, acute predominant signs and symptoms (vomiting, diarrhea, and nausea) and duration of symptoms, approximately 48 hours, reported in this investigation are typical of Norovirus outbreaks. The pattern of illness onset dates indicated a person-to-person route of transmission rather than foodborne or another point source.

Norovirus is characterized primarily by abrupt onset of nausea, vomiting and/or diarrhea, headache, body aches, chills, but little or no fever.¹ The incubation period for Norovirus is 24-48 hours. Illness usually resolves on its own within 1-2 days without complications. Dehydration may result after prolonged vomiting and diarrhea, particularly in young children, the elderly, and those with weakened immune systems. Norovirus infections typically occur during cooler months of the year (October to April), but can occur year-round.

Norovirus is thought to be responsible for 50 percent of all foodborne gastroenteritis outbreaks.² The mode of transmission is fecal-oral, and persons are infected by contaminated food or water, through close contact with an infected person, or contact with contaminated environmental surfaces and fomites. Because studies indicate Norovirus can become aerosolized during the cleaning process of infected vomitus, and stool, it is recommended a mask be worn for protection while cleaning restrooms, vomitus or stool. Norovirus, which is shed in stool, is highly contagious, and an infectious dose can contain as little as 100 viral particles.¹ Persons with Norovirus usually become infectious when symptoms begin and can continue to shed in their stool for up to 2 weeks or longer. Up to 30 percent of individuals infected with Norovirus are asymptomatic. Norovirus survives chlorine up to 10 ppm (above levels recommended for swimming pools and public water systems) ¹ and temperatures below 32ºF and up to 140ºF. Although the virus does not multiply outside the human body, it can survive readily on environmental surfaces for 24-48 hours.

Recommendations

Outbreaks caused by Norovirus can be prevented by strictly adhering to the following prevention measures:

Thoroughly wash hands with soap and clean running warm water (at least 100°F) for a minimum of 20 seconds after using the restroom, after assisting someone using the restroom, or caring for people ill with diarrhea and/or vomiting, after cleaning a restroom, before eating, and before preparing or serving food. Waterless antiseptic agents significantly reduce the number of microorganisms on skin but are not effective in eliminating Norovirus.

Persons with diarrhea and/or vomiting should not prepare food for others and should limit direct contact with others as much as possible.

Persons ill with diarrhea and/or vomiting should not attend meals and activities with other residents not experiencing symptoms.

The Indiana State Department of Health extends its appreciation to the Shelby County Health Department and the staff members of Ashford Place for their quick response and professionalism. Their prompt and appropriate actions were instrumental in ending this outbreak. Swiftly implemented control measures taken by Ashford Place on December 18, 2006, prevented the infection from spreading throughout the rest of the facility.

References

“Norwalk-Like Viruses” Public Health Consequences and Outbreak Management. Centers for Disease Control and Prevention. MMWR, June 1, 2001 50(9); 1-17.